Risk of ischemic stroke after cancer diagnosis: a population-based matched cohort study

Background — There are limited data regarding the association between cancer and ischemic stroke, particularly among individuals with previous stroke. Our objective was to measure and compare the risk of ischemic stroke in individuals with and without cancer.

Methods — Population-based matched cohort study in Ontario, Canada. Participants ≥18 years with a new diagnosis of cancer were matched (1:1) to cancer-free controls by age and sex in two separate matched cohorts based on the absence (Matched Cohort 1) or presence (Matched Cohort 2) of prior ischemic stroke. The primary outcome was the incidence of ischemic stroke. We calculated sub-distribution adjusted hazard ratios (aHR) and 95% confidence intervals (CI) for ischemic stroke (death as a competing event).

Results — In Matched Cohort 1, the rate and risk of ischemic stroke were higher among 620,647 cancer patients versus 620,647 controls at 1.5 years (4.6/1000 person-years [95%CI 4.5-4.7] vs 3.5/1000 person-years [95%CI 3.4-3.6], aHR 1.40, 95%CI 1.34-1.47). In Matched Cohort 2, the rate and risk of ischemic stroke were similar among 13,924 cancer patients and 13,924 controls at 1.5 years (26.9/1000 person-years [95%CI 25.1-28.9] vs 22.0 /1000 person-years [95/%CI 20.7-23.4]; aHR 1.00, 95%CI 0.88-1.14). In both cohorts, the risk of ischemic stroke was lower in cancer patients versus controls from 1.5 to 5 years (aHR 0.72, 95%CI 0.69-0.74 and aHR 0.53, 95%CI 0.46-0.62).

Conclusions — Compared to cancer-free controls, the rate and risk of ischemic stroke were higher 1.5 years after cancer diagnosis in individuals without prior stroke and varied according to cancer site and stage.